The present invention relates to a novel refrigeration cycle system usable in a rapid freezing refrigerator, for example.
A conventional refrigeration cycle system is shown in FIG. 1, in which a compressor 1, a condenser 2, first and second expansion devices 3a, 3b such as capillary tubes, an electromagnetic valve 4 connected in parallel with the first expansion device, and an evaporator 5 are coupled to each other in a series circuit. A single refrigerant, for example, Ccl.sub.2 F.sub.2 (di-chloro di-fluoro methane) or "R12", whose boiling point is -22.degree. F., is charged into the system, and circulates in the direction of the arrows.
A rapid freezing refrigerator must provide two freezing or refrigerating modes, a super-low temperature mode (-40.degree. F.--58.degree. F.) at the time of rapid freezing and a normal low temperature mode (5.degree. F.--4.degree. F.) at the time of ordinary freezing.
In the ordinary freezing mode the valve 4 is open, and the refrigerant gas brought to a high temperature and pressure state by the compressor 1 is first cooled and liquefied in the condenser 2. Such liquid thereafter flows through the second expansion device 3b via the valve 4, bypassing the first expansion device 3a, whereby it is brought to a low temperature and pressure state. The liquefied refrigerant is then fed through the evaporator 5 and gasified therein, and the refrigerant gas from the evaporator is finally returned to the compressor. Such ordinary freezing at a relatively high temperature (5.degree. F.--4.degree. F.) is performed endothermically in the evaporator 5.
In the rapid freezing mode the electromagnetic valve 4 is closed and the high temperature and pressure refrigerant gas from the compressor is cooled and liquefied in the condenser 2 in the same manner as above. Subsequently, the liquid refrigerant flows through both the first and second expansion devices 3a, 3b in which lower temperature and pressure states than before are obtained, whereafter rapid freezing to a super-low temperature (-40.degree. F.--58.degree. F.) is implemented in the evaporator 5.
Thus, in the conventional refrigeration cycle system the switching between the ordinary and rapid freezing modes is easily performed by opening and closing the electromagnetic valve 4. There is a general tendency in such a system, however, for the refrigerant pressure to decrease in proportion to the lowering of temperature, with the result that the refrigerating power will be lowered. Consequently, since a single fluid such as a pure refrigerant or an azeotropic refrigerant mixture is used in the conventional system, if it is selected to be most suitable for the ordinary freezing mode, for example, it lacks refrigerating power during the rapid freezing mode, and vice versa.